Is the scanned image black and white, and so should be compressed with CCITTG4 compression, or colour, which will have no compression with the settings above? That is assuming those settings, rather than scanner settings, determine the compression used.

Are the pixel dimensions of the two images the same?

You can check the pixel dimensions and compression used for each image using the Properties icon on the viewer toolbar...

So the two images are both black and white and have the same pixel dimensions, but the scanned image has no compression...

I haven't scanned from within XnView MP and can't easily try, but when I scanned from within another software some time ago I think it opened the normal scanner manufacturer's interface where the scan setting would be entered, you don't see that?

When a scan completes, is the image open in XnView MP, in which case when you save it the settings on the menu in your first post should apply, or when the scan completes is the result a file, in which case the scanner interface should have a way of selecting the file format and compression used?

I've downloaded your TIFF, opened it in XnView MP 93.1, and saved it with File > Format settings... > Write tab -- TIFF set to Black and white -- CCITT G4 (as in the screenshot your first post) and the resulting TIFF file has a filesize of 15.8Kb...

So confusing, and as I say I can't easily scan from XnView MP, but also you haven't answered some of my questions in my previous post, people in general often are not very good at that!